Electrical contact material containing silver,cadmium oxide,tin and nickel

ABSTRACT

ELECTRICAL CONTACT MATERIAL DISCLOSED CONTAINING SILVER, CADMIUM OXIDE, TIN AND NICKEL HAVING A MICROSTRUCTURE OF CADMIUM OXIDE PARTICLES DISPERSED IN A SILVER MATRIX WHICH ARE FINE AND FIBROUS. THE FIBROUS STRUCTURE GENERALLY OCCURS NORMAL TO THE OXIDIZED SURFACE.

arch 26, 1974 3,799,771

ELECTRICAL conmc'r MATERIAL conmmxnqsnvsx, CADMIUM L A $1 D C7 A H R A wH mw 5 ETD 2 .d 6 K e 6 A M1 1 T In I F m F United States Patent Oflice.

3,799,771 Patented Mar. 26, 1974 U.S. Cl. 75-178 A 15 Claims ABSTRACT OFTHE DISCLOSURE Electrical contact material is disclosed containingsilver, cadmium oxide, tin and nickel having a microstructure of cadmiumoxide particles dispersed in a silver matrix which are fine and fibrous.The fibrous structure generally occurs normal to the oxidized surface.

BACKGROUND OF THE INVENTION The present invention relates to new anduseful improvements in a silver-cadmium oxide electrical contactmaterial used for electrical contacts. 7

In general, silver-cadmium oxide electrical contact materials arecharacterized by being more resistant to sticking and resistant toerosion than silver electrical contact material, and the contactresistance is stable, so they are used widely for light current loadsand medium-heavy loads.

Such silver-cadmium oxide electrical contact materials are manufacturedby a powder metallurgical process, by a post oxidation process, or by apreoxidation process. The powder metallurgical process is a process inwhich a moulded mixture of silver powder and cadmium oxide powder issintered, as described in greater detail, for example in U.S. Pat.2,145,690. The post oxidation process comprises preparing asilver-cadmium alloy, working it to desired shape and heating it inoxidizing atmosphere so as to have cadmium thereof selectively internaloxidized. 'Further information may be found in U.S. Pats. 2,539,298 and2,673,167. The pre-oxidation process, described in U.S. Reissue Pat.27,075 and U.S. Pat. 3,545,- 067 involves forming fine particles ofsilver-cadmium alloy, for example by atomizing a melt of silver-cadmiumalloy, internally oxidizing the cadmium in the particles, consolidatingthe oxidized particles and mechanically working to desired shape.

However, silver-cadmium oxide electrical contact materials are oftenunsatisfactory in regard to resistance to erosion and in breakingcharacteristics.

Therefore an object of the present invention is to provide an improvedelectrical contact material having a lower erosion rate. Another objectof the present invention is to provide a contact material havingimproved hardness.

Another object of the invention is to provide a contact material havingimproved hardness at elevated temperature.

Another object of the present invention is to provide a contact materialhaving lower sticking power.

Another object of the invention is to provide a contact material whichhas a stable contact resistance.

Other objects will be apparent from the following description anddrawings wherein:

FIG. 1 is a photomicrograph of the microstructure of the electricalcontact material of the present invention at 200 magnifications,containing 13% CdO, 1.0% Sn and 0.02% Ni.

FIG. 2 is a photomicrograph of the microstructure of post oxidized priorart contact material and containing silver cadmium oxide at the samemagnifications as FIG.

1 and having the same cadmium oxide compositions as the material of FIG.1.

FIG. 3 is a photomicrograph of electrical contact material of the priorart containing, silver, cadmium oxide and tin at the same magnificationsas FIG. 1 with the same composition of cadmium oxide and tin as thematerial of FIG. 1.

SUMMARY OF THE INVENTION The electrical contact characteristics ofsilver-cadmium oxide electrical contact material are improved by addingabout 0.2 to about 5%"tin and about'0.005 to 0.5%

nickel to the material. The microstructure comprises fine and fibrousgrains of cadmium oxide precipitated in a silver matrix.

Preferably the material contains about 0.3 to 2% tin and about 0.01 to0.3% nickel.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates toan electrical contact material manufactured by oxidizing asilver-cadmium alloy prepared by adding 0.2 to 5% tin (weight andhereinafter in this application) and 0.05 to 0.5 nickel tosilver-cadmium to provide a material consisting essentially of up to 30%cadmium, about 0.2 to about 5% tin, about 0.005 to about 0.5% nickel,the balance silver.

The addition of tin has the effect of causing the configuration of thegrains of cadmium oxide during selective oxidation to be a fibrousstructure normal to the oxidized surface as shown in FIG. 3. The addedamount of tin under 0.2%, however, does not make the effect of theaddition distinguishable and an amount over 5% increases theprecipitation of cadmium at the grain boundary, reducing the electricalconductivity and workability of the alloy' considerably. Preferably thetin content is from about 0.3 to about 2%.

The addition of nickel is effective in causing the grains of cadmiumoxide after the internal oxidation of the silver-cadmium alloy to beremarkably fine as can be seen from comparing FIGS. 1 and 3. The cadmiumoxide particles are generally not larger than LIMP x 10a. The addedamount of nickel under 0.005% does not make the effect of the additiondistinguishable. Nickel, however, is only slightly solid soluble insilver and cadmium, so its added amount is not above about 0.5Preferably the nickel content is from about 0.01 to about 0.3%. Thepreferred material consists essentially of about 5 to about 15% cadmium,about 0.3 to about 2% tin, about 0.01 to about 0.3% nickel, the balancesilver.

The electrical contact material of the present invention may bemanufactured for example by either the postoxidation or pre-oxidationtechniques mentioned above.

In regard to the pre-oxidation technique, U.S. Reissue Pat. 27,075 andU.S. Pat. 3,545,067 are hereby incorpo rated into the presentapplication by reference and may be referred to for exemplary processingparameters which may be used in processing according to this technique.

In utilizing this technique the nickel and tin may be added to thesilver melt prior to atomizing. An excess of tin and nickel may be addedto allow for any losses of tin and/or nickel while adding these elementsto the melt and/or during pouring.

The tendency for the fibrous structure to appear normal to the oxidizedsurface is often lost in this technique. While the fibrous structure isnormal to the oxidized surface within individual particles, since theseparticles are randomly consolidated and are subsequently mechanicallyworked, the fibrous structure becomes random throughout themicrostructure.

In regard to the post oxidation technique, U.S. Pats. 2,539,298 and2,673,167 are hereby incorporated into the present application byreference for their description of exemplary temperature ranges andother processing parameters which may be used in processing according tothis technique. The tendency for the fibrous structure to be normal tothe oxidized surface is greater when this technique is used than withthe pre-oxidation technique because the oxidation step occurs after thearticle has been formed so that the tendency for the fibrous structureto be normal to the oxidation face is not lost through consolidation ofoxidized particles and/or mechanical working to shape.

In general, in oxidizing the fine particles according to thepre-oxidation technique, or the finished or semi-finished shapeaccording to the post-oxidized technique, an oxidation temperature ofabout 700 to about 850 C. and

V a time of about to about 1 50 hours is preferred, de-' pending uponsection size, oxidizing temperature, and oxygen content of theatmosphere.

The hardness of the electrical contact material is greater than priorart material of similar cadminum oxide composition without nickel. It isreally at least about 50% higher at room temperature and is often twiceas hard. The hardness at elevated temperature is also improved at leastabout twice and is usually as hard as prior art material of similarcadmium oxide composition.

Also the arc erosion rate and sticking power are lower with the materialof the present invention. The arc erosion rate is usually at least 25%lower and often 50% or more lower. The sticking is usually at least 50%lower and is often three times lower.

SPECIFIC EMBODIMENTS -An alloy comprising 13.3% cadmium oxide, 0.45% tinoxide, 0.03% nickel oxide and the balance silver is manufactured byadding 12.0% cadmium, 0.5% tin, and 0.5% nickel to a silver melt androlling the resulting casting to sheet form having a thickness of 1.5mm. and then heating it at 700 C. for 96 hours in an oxygen containingatmosphere. The electrical conductivity and hardness of saidsilver-cadmium oxide alloy are shown in Table 1, together with those ofanother alloy as a comparative material prepared under the sameconditions as above by adding 13.3% cadmium oxide to silver.

TABLE 1 Electrical conductivity, Sample IACS, percent Hardness, HRF

NOTE.-A:The contact material according to the present invention. B=Thecomparative material.

TABLE 2 Eroded amount Contact resist- (mg.) after ance (m9) after500,000 times 500,000 times Sample of switching of switching No'rE.A=Thecontact material to the present invention. B=the comparative material.

Test conditions:

Voltage: 200 v. Current:

at making, 47 A., pf. 0.35 at breaking, 235 A., pf. 0.65 Switchingfrequency: 20 time/ min.

Moreover, the results of the stick test carried out with the contactmaterial according to the present invention and the comparative materialrespectively each in the shape of the contact having the diameter of 6mm. and the thickness of 1.5 mm. are shown in Table 3.

TABLE 3 Number of Sticking Eroded times of power amount Sample switching(kg.) (mg.)

A 10 1. 3 6. 5 B i 12.0 i 32. 0

1 Stuck at 7th time.

The eroded amount of the contact material according to the presentinvention is about half that of the comparative material (not added withtin and nickel) as shown in Table 2, and Table 3 shows that the stickingpower of the former is about one-ninth of that of the latter in thestick test under the current 2000 A. Therefore, the contact materialaccording to the present invention has improved antierosive andantisticking properties.

As shown above, the silver-cadmium oxide electrical contact materialaccording to the present invention is industrially very favorable due toits improved contact characteristics.

What is claimed is:

1. Ag-CdO type electrical contact material having improved hardness anderosion rate, the material consisting essentially of an effective amountup to 30 wt. percent Cd, about 0.2 to about 5 wt. percent Sn, about0.005 to about 0.5 wt. percent Ni, and the balance Ag, the materialbeing oxidized to convert oxidizable constituents to their respectiveoxides prior to use as an electrical contact material.

2. The Ag-CdO type electrical contact material of claim 1, wherein theCd content is from about 5 to about 15 wt. percent, the Sn content isabout 0.3 to about 2 wt. percent, and the Ni content is about 0.01 toabout 0.3 wt. percent.

3. The Ag-CdO type electrical contact material of claim 1, wherein themicrostructure of the contact material comprises CdO grains in an Agmatrix in which CdO grains are fine and fibrous.

4. The Ag-CdO type electrical contact material of claim 3, wherein thefibrous structure of the CdO grains is substantially normal to theoxidized surface of the contact material.

5. The Ag-CdO type electrical contact material of claim 4, wherein theCdO particle size is not generally larger than I p x 10;.

6;. The Ag-CdO type electrical contact material of claim 2, wherein theSn content is greater than about 0.5 wt. percent but less than about 2wt. percent.

7. A method of making the Ag-CdO type electrical contact material ofclaim 1 comprising the steps of providing a melt of Ag-Cd-Sn-Ni to forma body consisting essentially of an effective amount up to 30 wt.percent Cd, 0.2 to 5 wt. percent Sn, 0.005 to 0.5 wt. percent Ni, thebalance Ag, and subjecting the body to oxidation to 5 convert oxidizableconstituents to their respective oxides and form the contact material,the Sn and Ni constituents cooperating to cause grains of CdO to be fineand fibrous.

8. The method of claim 7, including the further step of causing grainsof CdO to be substantially normal to the oxidized surface of the contactmaterial.

9. The method of claim 7, wherein the body is subjected to oxidationprior to forming a contact shape.

10. The method of claim 8, including the further step of forming thebody into a cast shape having the thickness of the contact materialprior to subjecting the cast shape to oxidation.

11. The method of claim 8, wherein the CdO particle size is about 1a x10 or less.

12. The method of claim 10, wherein Cd-Sn-Ni are added to a melt of Ag.7

13. A method of making the Ag-CdO ty-pe electrical contact material ofclaim 2 comprising the steps of forming an Ag melt, adding to the Agmelt Cd-SIl-Ni to form a body consisting essentially of 5 to 15 wt.percent Cd, 0.3 to 2 wt. percent Sn, 0.01 to 0.3 wt. percent Ni, thebalance Ag, subjecting the body to oxidation to convert the oxidizableconstituents to their respective oxides, and causing the grains of CdOto be fine and fibrous and normal to the oxidized surface therebyforming the electric contact material.

14. The method of claim 13, wherein the CdO particle size is about Imp x10 or less.

15. The method of claim 14, wherein the Sn is more than about 0.5 wt.percent but less than about 2 wt. percent.

References Cited UNITED STATES PATENTS 3,607,244 9/1971 Kabayama et a1.75--173 R L. DEWAYNE RUTLEDGE, Primary Examiner E. L. W-EISE, AssistantExaminer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 3,799,771 Dated 03/26/74 Inventor(s) Takeo Harada It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Col. 2 line 2 3'delete-0.05 after and insert---0.00 5- Col. 2, line 27delete--0. 00.5. after about. insert-"0.05 5

Signed and sealed this 5th day of Novefnlger 1974 (SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM PC4050 (lo-69) USCOMM'DC 60376-P69 [1.5. GOVERNMENTPRINTING OFFICE: ll 0-368-3JL I UNITED STATES PATENT OFFICE ICERTIFICATE OF CORRECTION Patent No. 3,799,771 Dated 03/26/74Inventofls) 'I'akeo Harada It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Col. 1, line"28, delete current after light. Insert currentaftermedium-heavy.

Col. 2, line 23 de1ete-0.05 after and insert--0.005-- Col. 2, line 27delete--0.00.5 after about insert--0. 05 f Signed and sealed this 5thday of Novefnl er 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM powso uscoMM-oc 60376-P69 9 L5- GOVIRNNENT PRINTING OFFICE2 I". 3"'-ll,

